Not Applicable
Not Applicable
The present invention relates to electromechanical devices having laminate structures and methods for fabricating such devices. More particularly, the present invention relates to laminate-based electromechanical relay devices and methods for fabricating such relays. However, the present laminate-based fabrication method may be suitably adapted for use in connection with the design and fabrication of a wide variety of laminate-based electromechanical devices. Accordingly, an example of a possible application of the laminate-based fabrication method and apparatus of the present invention includes the design and fabrication of high frequency range electromechanical relay devices.
Conventional electromechanical devices, such as electromechanical relays, have traditionally been fabricated one individual device at a time, by either manual or automated processes. The individual devices produced by such an xe2x80x9cassembly-linexe2x80x9d type process generally have relatively complicated structures and exhibit high unit-to-unit variability. Such variability is undesirable because it limits the repeatability of performance from unit-to-unit. In particular, in the case of relays used to switch high frequency signals, such variances in physical geometry may result in changes in the device""s inductance and capacitance, rendering such a device undesirable. While conventional electromechanical relays can be designed to reduce unit-to-unit variability, the resultant device is typically more costly to manufacture. Conventional electromechanical relays are also relatively large when compared to other electronic components. Size becomes an increasing concern as the packaging density of electronic devices continues to increase. Combined, these shortcomings render such conventional electromechanical relay devices undesirable.
A number of efforts at combating these and other shortcomings have focused on fabricating electromechanical devices, such as electromechanical relays, using silicon-based microfabrication techniques. Microfabrication, also known as micromachining, commonly refers to the use of known semiconductor processing techniques to fabricate devices known as microelectromechanical systems (MEMS) devices. Typical MEMS devices include motors, actuators and sensors. In general, known MEMS fabrication processes involve the sequential addition or removal of layers of material from a substrate layer through the use of thin film deposition and etching techniques until the desired structure has been achieved. Accordingly, MEMS devices typically function under the same principles as their macroscale counterparts. However, advantages in design, performance, and cost typically are also realized due to the great decrease in scale MEMS devices offer over their macroscale counterparts. In addition, due to the batch fabrication techniques employed to fabricate MEMS devices, significant reductions in unit-to-unit variation and per unit cost are also typically realized.
As noted above, MEMS fabrication techniques have been largely derived from the semiconductor industry. Accordingly, such techniques allow for the formation of a variety of micromechanical structures using adaptations of patterning, deposition, etching, and other processes that were originally developed for semiconductor fabrication. In general, these processes start with a wafer of silicon, glass, or other inorganic material. Multiple devices are then fabricated from the wafer through sequential addition and removal of layers of material using such techniques. Once complete, the wafer is sectioned (diced) to form the multiple individual MEMS devices (die). The individual devices are then fitted with external packaging to provide for electrical connection of the devices into larger systems and components. Again, the processes used for external packaging of the MEMS devices are analogous to those used in semiconductor manufacturing.
As an example, in the case of the moving contact of a MEMS relay, the moving contact may be formed using either surface micromachining techniques, bulk micromachining techniques, or a combination of the two techniques. In an example of surface micromachining techniques, an underlying layer, formed from an electrically conducting metal such as copper or gold, is defined, patterned, and deposited on the surface of a substrate typically formed from silicon, glass, or quartz. Through a photoresist process, a beam structure, typically formed from nickel or gold, is defined, patterned, and deposited on the surface of the underlying layer. The photoresist sheet is then removed, forming the actual structure of the beam. After the portion of the underlying layer that sits beneath the beam structure has been etched away, the resultant freestanding beam forms the moving contact of the relay. In an example of bulk micromachining, a free standing beam is formed from the layer of conducting material by deep etching of the underlying silicon, glass, or quartz substrate. The resulting beam structure is then plated with a layer of electrically conducting metal such as gold or copper. The resultant freestanding beam forms the moving contact of the relay.
MEMS devices have the desirable feature that multiple MEMS devices, or die, may be produced simultaneously in a single batch by processing many individual components on a single wafer. For example, using either surface or bulk micromachining, numerous individual relay devices may be formed on a single wafer of silicon. Once fabrication is complete, the substrate is typically diced to produce individual die. Each die typically contains a single relay. The individual relays may then be packaged in the same manner as semiconductor, for example, on a lead frame or chip carrier. Accordingly, the ability to produce numerous devices in a single batch results in a cost savings over the xe2x80x9cone outxe2x80x9d or xe2x80x9cassembly linexe2x80x9d style typically used by macro scale production techniques. The use of batch processing also increases the throughput of the MEMS fabrication process, while decreasing the overall variation between the individual die fabricated in each batch. In the specific example of electromechanical relays fabricated using MEMS fabrication techniques, batch processing has the advantage of increasing the uniformity of MEMS relay devices, decreasing the size of the devices, and reducing the cost associated with the fabrication and processing of the devices.
However, MEMS fabrication techniques are not without their drawbacks. In the example of electromechanical relays, the physical properties of the silicon, quartz, and glass substrates on which the MEMS relay devices are typically fabricated are not well suited in general to the demands placed on them by the design of an electromechanical relay. In particular, it is important to the operation of an electromechanical relay that the contacts on the relay be fully isolated when the relay is in the open position, such that no signal is carried across the relay, and that there be no isolation or resistance between the contacts when the relay is in the closed position, such that the signal is carried undistorted across the relay. Due to the reduced scale of MEMS devices, and the materials and processes used in MEMS fabrication, MEMS devices do not easily lend themselves to vertical processing. Accordingly, the physical spacing, and thus the signal isolation, between the contacts in a MEMS relay is often insufficient to fully isolate the contacts when the relay is in the open position. Thus, MEMS relays often exhibit an unacceptable flow of current across the contacts when the relays are in the open position. This problem is particularly apparent when the relays are used to switch high frequency signals. The ability of MEMS relays to operate at high frequencies may also be reduced by the dielectric properties of the material employed to fabricate the MEMS relay. Silicon, for example, has a relatively high microwave loss tangent, thereby limiting the performance at high frequencies of devices formed from silicon.
Further, particularly in many high frequency applications, it is desired that a relay behave as a controlled impedance structure. In particular, when relays, or other electromechanical devices, are intended for operation at very high frequencies, the electrical parameters of the structures from which the relay is constructed (e.g. resistance, inductance, and capacitance) will affect the overall frequency response of the relay. For a given frequency, or over a given range of frequencies, the impedance of a relay is determined by these electrical parameters. Thus, given the variations in material and construction between the electromechanical structures from which a relay is constructed (e.g. input connections, moving contact, stationary contact, output connections, etc.), each of the structures from which the relay is constructed may exhibit a different impedance. Such variations in impedance at the transition points between the various structures of the relay (typically called xe2x80x9cmismatchesxe2x80x9d) can adversely affect performance of the relay at certain frequencies. For example, over a given range of frequencies, a mismatch may cause the signal carried by the relay to become attenuated and/or the waveform of the signal to become distorted, thus rendering the relay unsuitable for certain applications.
In traditional macroscale relay devices, such mismatches are avoided by choosing the materials from which the relay is constructed so as to minimize the variations in impedance throughout the various structures of the relay for the range of frequencies at which the relay is to be operated. For example, the input and output connections may be formed as a transmission line structure in which the impedance of the signal conductor is referenced to the impedance of the ground conductor. Examples of common transmission line structures include: (a) Coaxial, in which the signal conductor is the center conductor, and the ground an outer shield and the center conductor is separated from the shield by dielectric material; (b) Microstrip, in which the signal is carried on a rectangular cross-section conductor separated from a ground plane layer by dielectric material; (c) Stripline, in which the signal conductor is sandwiched between two ground planes (with dielectric separation); and (d) Co-planar waveguide, in which the signal conductor and two parallel adjacent ground conductors are patterned on the same dielectric substrate. The ideal transmission line has a characteristic impedance that is independent of the location along the transmission line. As such, a macroscale relay device that is to be operated over a range of high frequencies will ideally be designed to exhibit a specific impedance over the range of frequencies of operation throughout its entire transmission line. Such a transmission line structure is commonly referred to as a controlled impedance structure.
However, MEMS devices may be fabricated on only a limited number of substrate materials. As previously noted, such materials often exhibit unacceptable performance characteristics when used in devices designed to function at high frequencies. Thus, such devices often require additional or secondary packaging to overcome these shortcomings in performance. The need for secondary packaging represents a significant disadvantage to the use of MEMS fabrication techniques in relay applications. In particular, after MEMS relay devices have been processed, the individual die are typically each transferred to a separate substrate or lead frame. The lead frame provides for the electrical connection of the relay to other devices by, for example, a ball grid array or a pin grid array. This secondary packaging step is highly undesirable due to the additional cost of the lead frame and packaging step, such cost will often exceed the cost of the relay itself. In addition, the potential yield loss in the resulting packaged device and the potential performance limitations that may result in the packaged device due to the creation of impedance mismatches between the device and the package are also quite undesirable.
The present invention is thus directed to a method of fabricating electromechanical devices such as relays, which addresses, among others, the above-discussed needs and provides a low cost electromechanical device that exhibits consistent and superior performance and operation at increased frequency ranges when compared with currently available devices.
In accordance with the present invention, there is provided a method of fabricating laminate-based electromechanical devices and the laminate-based electromechanical devices resulting therefrom. Unlike the known methods of fabrication of MEMS devices, the laminate-based fabrication method of the present invention includes fabricating component electromechanical structures of an electromechanical device from individual layers of laminate material using, for example, materials and processes from the art of semiconductor and printed circuit board manufacturing, followed by the joining of the individual layers of laminate material to form a unitary laminate electromechanical device. Additionally, the present invention is directed to a method that includes joining individual layers of laminate material to form a unitary laminate structure, followed by the fabricating of an electromechanical device from the unitary laminate structure using, for example, processes from the art of semiconductor and printed circuit board manufacturing. The present invention is further directed to a method of fabrication that employs various combinations of fabricating the component electromechanical structures of an electromechanical device from individual layers of laminate material using, for example, materials and processes from the art of printed circuit board manufacturing, and combining the individual layers of laminate material to form a unitary laminate electromechanical device. When applied to the fabrication of electromechanical relays, the present invention thus allows for greater optimization of the materials used in the fabrication of the device so as to allow the device to perform as a controlled impedance structure over a range of high frequencies. The present laminate construction technique also results in an electromechanical device that includes integral packaging and thus does not require secondary packaging operations.
In the case of a laminate-based electromechanical relay device fabricated using the method of the present invention, an embodiment of that method involves the fabrication and sequential lamination of component electromechanical structures, including, for example, conductors, contacts, and actuators, formed from individual layers of dielectric materials, to form a unitary three-dimensional laminate structure. In particular, actuators, leads, connectors, conductors, contacts, and other electromechanical structures of the relay may be defined by subtractive processes known in the art of semiconductor and printed circuit board fabrication, such as, for example, photodefinition and etching of an electrically conducting material clad on a layer of laminate material. Alternatively, such electromechanical structures may be formed by additive processes known in the art of semiconductor and printed circuit board fabrication, such as, for example, de position of an electrically conducting layer on a layer of laminate material. Further fabrication processes known in the art of semiconductor and printed circuit board fabrication, including, for example, laser ablation or drilling, may also be employed to create such electromechanical structures.
The present laminate based fabrication method thus represents an improvement upon existing fabrication methods by permitting for the use of a wider range of materials and thereby increasing the range of materials that may be used to optimize the performance and current carrying capacity of the device for use in high frequency applications.
The present laminate-based fabrication method represents a further improvement upon existing fabrication methods by increasing the ability to use vertical processing to fabricate laminate based electromechanical devices having layers of increased thicknesses, and thereby increasing the physical separation and electrical isolation between layers.
The present laminate-based fabrication method represents yet another improvement over existing fabrication methods by providing the ability to fabricate electromechanical devices having electrical contact surfaces of increased size and, therefore, increased current carrying capacity.
The present invention provides still another advantage over existing fabrication methods by allowing for fabrication of laminate-based electromechanical devices of a variety of transmission line structures that incorporate integral packaging of input/output connectors within the electromechanical device itself, thus eliminating the need for secondary packaging of the relay with input/output connectors.
The present invention represents another advantage in that it may also be utilized to imbed electromechanical devices directly into larger multi functional circuits and components during the fabrication process, thereby eliminating the need for ancillary processing and assembly. As such, the laminate-based electromechanical device fabricated of the present invention is self-packaging.
The present laminate based fabrication method provides a further advantage by allowing for the batch fabrication of multiple individual laminate-based electromechanical devices, of either identical or differing design, on a single laminated panel. The present invention additionally provides for the batch fabrication of multiple devices as part of a single component that contains various other laminate-based electromechanical devices that may be either electrically linked or unlinked.
The present invention also provides for the concurrent batch fabrication of multiple electromechanical devices electrically linked together in various arrangements to form a single component, such as a switch matrix. Thus, the present laminate-based construction method readily provides for three-dimensional interconnection of electromechanical devices.
The present invention thus provides another advantage because the surface area of the wafer on which the devices are fabricated need not be devoted to use by electrical interconnections. Thus, laminate structures, in which certain layers of the structure are dedicated to, for example, interconnection of the devices in the adjacent layers, are possible and the surface area of the wafer that may be occupied by the devices themselves is increased.
The present laminate-based fabrication method provides yet another additional advantage over existing MEMS fabrication methods by providing for the simultaneous fabrication of a relatively greater number of individual electromechanical devices in a single batch. Such advantage arises due to the increased available surface area of a typical printed circuit board panel relative to a typical substrate wafer used by other fabrication methods, where the size of a panel may be an order of magnitude greater than the other substrate. Thus, because a greater number of relays can be fabricated simultaneously on a single panel, the present laminate-based device provides economic advantages with respect to its existing counterparts by offering a reduced per unit cost.
Still additional economic advantages result from the present invention due to the relatively low costs associated with printed circuit board processing techniques as compared with other processing techniques. The laminate-based relay device thus achieves the advantages of mass production offered by existing fabrication methods, while providing additional versatility and potential economies.
Accordingly, the present invention provides for an improved method of fabricating electromechanical devices and results in laminate-based electromechanical device having improved function in, for example, high-frequency relay applications. In particular, the present invention provides for a method of fabricating a laminate-based relay device resulting in a laminate-based relay device capable of improved operation at high frequencies. The reader will appreciate these and other details, objects, and advantages of the present invention upon consideration of the following detailed description of embodiments of the invention, and may also comprehend such details, objects, and advantages of the invention upon practicing the invention.